class AppClass(list):
    def __init__(self):
        self.append(["Hello world!"])
    
    def __call__(self, environ, start_response):
        status = '200 OK'
        response_headers = [('Content-type','text/plain')]
        start_response(status, response_headers)
        return self
    
    def close(self):
        pass

application = AppClass()

  